Magnetically coupled pump with slip detection means



May 19, 1970 MAG J. LAW 3,512,901

NETICALLY COUPLED PUMP WITH -SLIP DETECTION MEANS Original Filed July28, 1967 2 Sheets-Sheet 1 INVENTOR. JOHN LAW. BY f ATTORNEY.

J. LATW May 19, .1970

MAGNETICALLY COUPLED PUMP WITH SLIP DETECTION MEANS Originai Filed July28, 1967 2 Sheets-Sheet 2 R. m E v JOHN LAW.

FIG. 2

ATTORNEY.

United States Patent M US. Cl. 417-53 Claims ABSTRACT OF THE DISCLOSUREA magnetic drive pump for use in an absorption refrigeration system,having coil disposed intermediate rotating drive and follower magnetsfor sensing resulting variation in the magnetic flux linking the coil toprovide a control signal indicative of loss of magnetic coupling.

CROSS REFERENCE TO RELATED APPLICATION This application is a division ofmy co-pending application Ser. No. 656,851, filed July 28, 1967, nowPat. No. 3,429,137.

BACKGROUND OF THE INVENTION This invention relates to a method anddevice for determining loss of magnetic coupling between magnetic driveand driven members, and more particularly to a magnetic drive pump foruse in an absorption refrigeration system.

In absorption refrigeration systems utilizing an absorbent such amixture of water and lithium bromide as an absorbent solution and wateras a refrigerant, separate circulation of absorbent and refrigerantfluids is commonly effected by means of a pump having hermeticallysealed impeller chambers at opposite ends of the pump motor. The pumpsmay desirably be magnetically coupled to the motor to obtain such fluidcirculation.

The present invention is applicable to absorption refrigeration systemsemploying magnetic driven pumps. In such a pump the driving motor iscoupled to an impeller encased in a hermetically sealed housing bymagnetic coupling through a non-magnetic diaphragm between permanentmagnets aflixed to the motor and the impeller to effect synchronousdrive. If the driven magnet slips or falls out of synchronism with thedrive magnet in synchronous magnetic drives, the coupling is lost andcannot be restored until the drive and driven magnets are stopped. Whenslip occurs, the impeller stops even though the drive motor continues torun. This can present an undesirable situation which may result inover-concentration of the absorbent solution or possibly solidificationof absorbent.

Heretofore, a method of sensing slip has been to monitor motor currentwhich decreases when slip occurs in the coupling. Motor current,however, is additionally a function of individual motor characteristics,line voltage and variations in load, and consequently, these additionalfactors present problems affecting the accurate detection of slip.

Accordingly, it is an object of this invention to provide an improvedabsorption refrigeration system having a magnetic drive pump forcirculating the system fluids.

It is a further object to obtain improved control of magnetic drivepumps in absorption refrigeration systems.

SUMMARY 'OF THE INVENTION The present invention is directed to amagnetic pump coupling having means which functions to detect the3,512,901 Patented May 19, 1970 occurrence of loss of magnetic couplingby sensing a variation in the magnetic flux pattern intermediate driveand driven magnets in the magnetic drive pump and associated circuitryto de-energize the pump motor, whereby the motor can come to a stop andpermit the magnetic coupling to become re-established.

'In accordance with a preferred embodiment of this in vention, anabsorption refrigeration system including an evaporator, absorber,generator, condenser, and a magnetic drive rotary pump for circulatingfluids in the system, is provided with a magnetic sensing device for determining loss of magnetic coupling between the pump drive magnet anddriven magnet. Circuitry is provided for controlling the refrigerationsystem pump by de-energizing the pump motor when coupling is lost toautomatically regain the coupling.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 illustrates a diagrammatic viewof a basic absorption refrigeration system including a partial crosssectional view of the magnetic pump coupling of the present invention;

FIG. 2 is a schematic diagram of a magnetic flux sensing detectorcircuit embodying the present invention, including a simplified viewshowing the magnetic drive and magnetic flux sensing coil arrangement;and

FIG. 3 is an enlarged sectional view taken along line III-III of FIG. 2showing the magnetic flux sensing C011.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring particularly to FIG.1, there is shown diagrammatically a basic absorption refrigerationsystem 10 suitable for practicing the present invention. The systemincludes condenser 11, generator 12, evaporator 13, absorber 14, heatexchanger 15 and a magnetically driven dual pump 16 connected to providerefrigeration.

Dual pump 16 comprises hermetic refrigerant pump 19, hermetic solutionpump 20 and pump motor 17. Weak absorbent solution, such as a solutionof lithium bromide and water is forwarded by solution pump 20 fromabsorber 14, through heat exchanger 15 to generator 12 where therefrigerant is boiled off to concentrate the absorbent solution. Theheated strong absorbent solution is returned to absorber 14 through heatexchanger 15 in heat exchange relation with the weak solution. Refrigerant vapor boiled off in generator 12 is condensed in condenser 11and the liquid refrigerant is then passed to evaporator 13. Unevaporatedrefrigerant accumulated at the bottom of evaporator 13 is recirculatedby refrigerant pump 19 and returned to evaporator 13 for evaporation toprovide a cooling or refrigeration effect for supplying a refrigerationload. The refrigerant vapor from evaporator 13 is absorbed by strongabsorbent solution in absorber 14, forming a weak absorbent solution.

As shown in FIG. 1, pump motor drive shaft 18 is keyed to hub 22 whichhas a cup-shaped flange 23 formed thereto. Secured within flange 23 is atoroidal shaped radial drive magnet 24 that has a number of alternatenorth and south pole radially-extending magnetized areas and magneticbacking plate 25. Radial driven magnet 26 is similar to radial drivemagnet 24- and is axially aligned opposite radial drive magnet 24 andmounted in face opposing relationship with a small separation gaptherebetween. Driven magnet 26 and backing plate 27 are secured incup-shaped flange 28 which is formed with impeller shaft 29. Bearing 30suitably aifixed to pump housing 34 is provided for qiournaling impellershaft 29. Contained within housing chamber 32 is an impeller 31 which isaflixed to impeller shaft 29 for propelling fluid. Non-magneticdiaphragm 40, which is mounted on casing 33 in the small gap betweendrive and driven magnets 24, 26, serves as an end closure hermeticallysealing the driven magnetimpeller portion from the drive-magnet motorportion of solution pump 20. Refrigerent pump 19 is similar to theconstruction of solution pump 20 differing only in function in therefrigeration system.

Diaphgram is composed of a rigid non-magnetic metallic material, such asthe iron-nickel alloy known as Iconel, so as not to short circuit themagnetic flux path from driven to drive magnets 26, 24 and to reduceeddy current losses which reduce the torque transmitting capability ofthe coupling.

Referring to FIG. 2, an enlarged simplified view is shown to illustratethe arrangement of diaphragm 40, drive magnet 24 and driven magnet 26.Supported by diaphragm 40 is a magnetic sensing coil 41. In thepreferred embodiment, as shown in FIGS. 2 and 3, magnetic sensing coil41 is of the printed circuit type, formed according to any well knownmethod on an electrically insulative substrate 43 that is impervious toa solution of water and lithium bromide. In order to permit arrangingdrive and driven magnets 24, 26 with a minimum gap therebetween andavoid physical contact with diaphragm 40, it is desirable to formmagnetic sensing coil 41 within a recessed portion of diaphragm 40 so asto be level with the surface of the diaphragm. The center terminus ofprinted circuit coil 41 is soldered directly to the diaphragm 40. Thusdiaphragm 40 serves as one connection to the coil through terminal 44. Asecond terminal 45 connects to the other end of coil 41. As shown inFIG. 2, magnetic sensing coil 41 is positioned to intercept magneticflux intermediate rotating drive and driven magnets 24, 26.

The operation of magnetic flux sensing coil 41 and its associateddetector circuit as shown in FIGS. 2 and 3, will now be considered.Under normal operating conditions with contacts 59 open and with driveand driven magnets 24, 26 rotating synchronously, a sinusoidal voltageis induced in magnetic sensing coil 41 from the effect of the motion ofmagnetic flux relative to coil 41 causing a time varying flux linkingthe coil. This induced sinusoidal voltage appearing at output terminals44 is applied to a voltage doubler comprising capacitor 51, diode 52,diode 53 and capacitor 54. The doubler output is then passed to relaycoil 56 through variable resistor 55. The voltage is suflicient to holdnormally open relay contacts 57 closed (after they have been initiallyclosed by other means as described below) when drive and driven magnets24, 26 are synchronized and running. The function of relay contacts 57,connected to the motor energizing circuit of absorptions refrigerationsystem control circuit 58, is to interrupt the pump motor energizingcircuit when slip is detected by circuit 50 and the voltage in relaycoil 56 falls below the normal operating level.

On start-up of absorption refrigeration system 10, time delay contacts59 are closed connecting detector circuit 50 to line AC. voltage sourceL L Half-wave voltage excitation from rectifier diode 61 and throughresistor 60, which are series connected with time delay contacts 59, isapplied to relay coil 56 when time delay contacts 59 are closed, throughvariable resistor 55, thereby closing contacts 57. Time delay contacts'59 open after a suitable, preferably five second delay, in thisparticular system, which is sufficient for synchronous drive and drivenmagnets 24, 26 to reach running speed and thereby provide a voltage incoil 41 and through circuit 50 to continue holding relay contacts 57closed after contacts 59 open.

As earlier mentioned, synchronous magnetic dual pump 16- is subject toloss of coupling or slip due to various causes such as impeller overloadand electric power transients. During synchronous rotation of drive anddriven magnets 24, 26 magnetic flux linking each magnetic pole of thenormally running radial magnets 24, 26 links sensing coil 41intermediate the magnets at a sinusoidal rate of change of flux linkageand thus induces a sinusoidal voltage therein. When slip occurs anddriven magnet 26 stops rotating, the rate of change of magnetic fluxlinking sensing coil 41 will be reduced by a factor of two because ofthe new flux condition existing in the gap between the magnets. This isobserved regardless of the relative position of sensing coil 41 withrespect to stopped driven magnet 26. This flux variation is such that asinusoidal voltage of one-half the peak-to-peak magnitude as induced inmagnetic sensing coil 41 under normal synchronous running conditionswill now appear at coil output terminals 44, 45. With the inducedvoltage reduced, the voltage applied to relay coil 56 is insufficient tohold relay contacts 57 closed, and when relay contacts 57 open, pumpmotor 17 is de-energized and stops. In practice, it is found desirableto include within system control circuit 58, control circuitryresponsive to sensing coil 41 output for shutting off the heating mediumsupplied to generator heat exchanger 36 upon the occurrence of slip inorder to prevent over-concentration and possible solidification ofabsorbent solution. Variable resistor is adjustable for setting the dropout voltage for contacts 57 according to the sensitivity of relay coil56.

Magnetic flux detector circuit 50 as shown in FIG. 2 is connected to asingle magnetic flux sensing coil 41. It should be noted that if it isdesired to sense slip in both pump sections of dual pump 16, twomagnetic sensing coils, one on each diaphragm 40, can be used in seriesor as dual inputs to a modified detector circuit, or as separate inputsto separate detector circuits.

While a preferred embodiment of this invention has been described forpurposes of illustration, it will be understood that other electricalcircuitry may be used to obtain the control functions described herein.It will be further understood that other types of magnetic fiux sensorsmay be employed at other locations on the magnetic coupling for sensingloss of coupling. Also, it is contemplated that automatic controlcircuitry may be incorporated for automatic restarting after stoppingdue to loss of coupling as described above.

While a preferred embodiment of the invention has been described, itwill be appreciated the invention is not limited thereto since it may beotherwise embodied within the scope of the following claims.

I claim:

1. A magnetic drive pump comprising:

(A) a motor;

(B) a magnetic drive member connected to the motor for rotational motiontherewith;

(C) an impeller;

(D) a magnetic driven member connected to the impeller and mounted forrotational motion with said magnetic drive member;

(E) an open ended housing enclosing said impeller and magnetic drivenmember;

(F) a non-magnetic diaphragm intermediate said magnetic drive andmagnetic driven members, said diaphragm secured to and closing the openend of said housing; and

(G) magnetic flux sensing means disposed intermediate the rotatablemagnetic drive member and rotatable magnetic driven member for sensingvariation in the rate of change of magnetic flux intermediate therotating magnetic drive member and magnetic driven member, said magneticflux sensing means providing a control signal when the rotation of thedriven member loses synchronous rotation with the drive member.

2. A magnetic drive pump as defined in claim 1 wherein said magneticflux sensing means is an electrical coil for providing an electricalcontrol signal for indicating the loss of synchronous rotation.

3. A magnetic drive pump as defined in claim 2 wherein said electricalcoil is a printed circuit coil.

4. A magnetic drive pump as defined in claim 2 wherein said electricalcoil is supported on the non-magnetic diaphragm adjacent said magneticdrive member.

5. A method of controlling a magnetic drive pump having an electricmotor, a control circuit connected to the motor, a magnetic drive memberattached to the motor for rotatable motion therewith, an impeller and amagnetic driven member attached to the impeller and mounted forrotational motion with the magnetic drive member, comprising the stepsof (A) energizing the pump motor for imparting synchronous motion energyto the pump impeller by a magnetic coupling force between the magneticdrive member and magnetic driven member;

(B) sensing variations in the magnetic flux intermediate the rotatingmagnetic drive member and magnetic driven member and providing a controlsignal incli- 6 cative of loss of synchronous rotation with the magneticdrive member; and (C) detecting the control signal and de-energizing themotor upon detecting loss of magnetic coupling to regain magneticcoupling between the magnetic drive member and magnetic driven member.

ROBERT M. WALKER, Primary Examiner US. Cl. X.R. 310104; 417-63, 420

